Method of mining

ABSTRACT

The danger of block caving in a mining operation is largely avoided through driving a number of drifts at suitable distances along the footwall, from which blast holes are drilled in such a manner, that after blasting a slot-shaped opening is obtained in the ore body along the footwall and in such a manner that as big a part as possible of the ore body is undercut e.g. through the arrangement of a fan-shaped pattern of blast holes, or a similar slot as described above from the drawpoints dipping towards the hanging wall, whereby the lowermost draft and a belonging drift which is driven adjacent and along the hanging wall of the ore body with connecting cross cuts are utilized as main loading level, which is completed with an additional, underlying loading level.

Fli 'iblll united States Patent [191 Haglund July 29, 1975 METHOD OF MINING Primary Examiner-Ernest R. Purser [75] Inventor' g zt gggg lz g Attorney, Agent, or Firm-Pierce, Scheffler & Parker [73] Assignee: Luossavaara-Kiirunavaara Aktiebolag, Stockholm, Sweden ABSTRACT [22] Filed: June 1, 1973 The danger of block caving in a mining operation is largely avoided through driving a number of drifts at [2]] Appl' 365854 suitable distances along the footwall, from which blast holes are drilled in such a manner, that after blasting a [30] Foreign Application Priority Data slot-shaped opening is obtained in the ore body alon g June 28, 1972 Sweden 8480 the footwell and in Such a manner that as big a P as possible of the ore body is undercut e.g. through the 52 us. 01. 299/13; 299/18; 299/19 arrangement of e fen-Shaped pattern of blast holes, or 51 Int. Cl. E21c 37/14 a Similar Slot as described above from the drawpoints [58] Field of Search 299/13, 19, 18; 102/23 dipping towards the hanging wall, whereby the lowermost draft and a belonging drift which is driven adja- 5 References Cited cent and along the hanging wall of the ore body with UNITED STATES PATENTS connecting cross cuts are utilized as main loading level, which is completed with an additional, underly- 473,734 4/1892 Forrester 299/13 ing loading level FOREIGN PATENTS OR APPLICATIONS I 232,176 11/1968 U.S.S.R 299/13 1 Clam" 1 Drawmg PATENTEI] JUL 2 9 I975 METHOD OF MINING Within mining there exist a number of well defined methods, each being adapted to special local conditions.

The present invention refers to such a mining method, called block caving.

Block caving is carried out in such a manner, that the ore is entirely or partially under-cut. The ore will cave, and can be loaded on a lower level. v

In order to avoid ore losses and dilution of waste rock it is important in this connection that drawpoints are arranged in a regular pattern and close-fitted.

In view thereof, the system of drifts and drawpoints is often complicated in block caving, which brings about a timeconsuming and expensive development work, which is difficult to mechanize.

This invention, a variant of block caving method, essentially simplifies this condition and makes a highgrade mechanization possible. This is achieved through a special construction with a double discharging level, which, seen from above, admits a more close-fitted location of drawpoints and facilitates the handling of boulders.

Undercutting of the ore body is achieved partly through cutting the ore along the footwall in connection with making a slot-shaped opening thereby drilling and blasting against an opening-raise from a number of drifts in the ore at suitable vertical distances along the footwall and partly in such a manner that as big part as possible of the ore body is undercut horizontally through blasting of e.g. a fan-shaped pattern of blast holes, drilled from the footwall drift at the upper discharging level, against a slot, which on its turn is blasted from the opening-raise at the footwall against the hanging wall.

The discharging level is performed so that a haulage drift is driven adjacent and along the hanging wall in the ore. This drift is connected by crosscuts (discharging drifts) with the slot at the footwall. This main discharging level is completed with another underlying additional discharging level, which is joined with the upper one through a slot at the footwall. For more close-fitted drawnpoints it is advantageous that the crosscuts of the lower level are staggered in relation to the crosscuts of the main discharging level.

In order to obtain an increased understanding of the invention, it will be examplified below with reference to the attached drawing.

In the ore 1, adjacent and along its footwall A-B-C-D a number of headings 2 are driven at suitable vertical distances, from which, except the one on the upper discharging level 5, blast holes are drilled in such a manner, that after the blasting against an opening-raise at the footwall a slot-shaped opening 3 is obtained along the same. This slot must not reach up to earlier brokenout area 4, which means that a roof 4 of a suitable thickness h must be left.

A loading level, which includes two drifts 5, of which one is included in the system of the above mentioned drifts 2 as the lowermost thereof is developed. The second drift 5 is positioned in the ore adjacent and along its hanging wall. The two drifts are connected between each other with regularly spaced crosscuts 6 driven angularly to it. The size of the headings and the distance between them can a.o. depend on the physical properties of the rock. Suitable centre distances between the crosscuts can be, for example, 8-15 m depending on the size of the drifts.

Under the said level, on a suitable level distance, for example 8-15 m, an additional discharging level 7 on the whole equally shaped is driven. It is, however, displaced in such a manner, that the underlying crosscuts are under the pillars of the main loading level lying above.

From the footwall drift of the upper discharging level holes are drilled, for example, according to a pattern 8, which is common in modern sublevel caving. Only two rows of holes are shown in the drawing.

Before blasting of slot and undercut can start, an opening-raise must be driven along the footwall, against which the first rows of holes are to be blasted. The opening can be carried out in the middle of the ore, in one end or in both ends of the ore. In the latter case two opening-raises are required.

The blasting is carried out in such a way that at first a fan-shaped slot 8 is blasted from the lowermost footwall drift 2 (S) straight across the ore from footwall towards the hanging wall. Then the slot along the footwall is opened from the upper situated footwall drifts 2. The blasting of the slot and undercut can thereafter be carried out simultaneously and continuously in a vertical front from all footwall drifts 2 retrograding with contemporary loading of overbroken ore in order to avoid compressed conditions for consequent blasting. At last or coincidently with the fan-shaped slot between the both discharging levels 5 and 7 is blasted. After a comparatively short time, some days or weeks, loading of caved ore can begin at a maximal rate until the ore thus prepared has been mined out.

Thereafter follows eventually a final mining in the conventional manner with sublevel caving of the rest of the ore.

The novelty of the method described is, that only a thin slice of the ore is removed nearest to the footwall of practically the entire main level besides conventional undercutting horizontally. The effect obtained thereby is that the ore caves and slides down to the loading places. The method does of course lead to the fact that the occurrence of boulders can be high at the beginning of the loading. During later drawing period the boulders are generally broken down during their sinking down with the caved ore. By the design with two loading levels handling of boulders and secondary drilling will to a great extent be facilitated, depending a.o. on the fact that many points of attack have been created. The boulder treatment is often a troublesome and even sometimes a dangerous work, which with this solution can be carried out under safe conditions for the operator. Also this arrangement of double loading levels used simultaneously is a novelty.

According to the present example, the loading levels have been positioned in the ore and the ore has been drawn relatively steeply. Naturally the said drift systems can be positioned in the footwall, which has been made according to an experiment in Malmberget, where part of the ore was taken out according to the invention with an extraordinarily successful result. If the ore is flat or wide the number of the loading levels can, of course, be increased, in order to avoid ore losses.

The sequential course of the present invention is:

I. Development drifting in the ore 7, including drifts 2 and 5 as well as crosscuts 6 and an additional discharging level 7 and also one or two opening-raises.

ll. Drilling of fan-shaped drill holes 8 from the drifts (2) of the footwall limit and simultaneously the approximately parallel holes directed upwards from the above situated drifts 2 and also from the foot-wall drift on the discharging level 7.

III. The blasting starts on level 5 with blasting of the fan-shaped bore holes 8, first forming a slot from the opening-raise at footwall across the ore against hanging wall and simultaneously blasting of the slot at the footwall between the two discharging levels 7 and 5. Thereafter the blasting of the slot 3 along the footwall can begin. The blasting continues then on all levels in the same vertical plane at a fairly hurried pace, for instance towards both ends of the ore body, if opening raise is situated in the middle of the ore, until the complete slot and undercut have been blasted. The rest of the ore is then developed for block-caving and the ore is caving and sliding down towards the discharging openings in the crosscuts.

IV. The discharging of the ore takes place immediately after the starting of blasting of the slots and undercut and continues then according to a carefully calculated pattern so that the interface between the ore and waste rock slides down as evenly as possible.

The described method has been proposed to be called slot blocking.

What is claimed is:

l. A method of mining ore fron an ore body (1) which comprises driving a number of drifts at suitable vertical distances along the footwall (2) of the body; drilling blast holes from said drifts through an arrangement of a fan-shaped pattern (8) of said blast holes partly in such a manner that, after blasting, a slotshaped opening (3) is obtained in the ore body along the footwall and partly in such a manner that as large part as possible of the ore body is undercut whereby a lowermost heading and an associated heading (5) with connecting crosscuts (6) are utilized as main discharging level, which main discharging level is supplemented with an additional underlying discharging level. 

1. A method of mining ore fron an ore body (1) which comprises driving a number of drifts at suitable vertical distances along the footwall (2) of the body; drilling blast holes from said drifts through an arrangement of a fan-shaped pattern (8) of said blast holes partly in such a manner that, after blasting, a slotshaped opening (3) is obtained in the ore body along the footwall and partly in such a manner that as large part as possible of the ore body is undercut whereby a lowermost heading and an associated heading (5) with connecting crosscuts (6) are utilized as main discharging level, which main discharging level is supplemented with an additional underlying discharging level. 